Conversion Of Citronellal Research Articles

A Study on Synthesis of para-menthane-3,8-diol (PMD) - A Safe Mosquito Repellent Active Ingredient

Active ingredient para-menthane-3,8-diol (PMD) is evaluated as effective in repelling insects in general and is recommended by the Centers for Disease Control and Prevention as an insect repellent, especially against mosquitoes worldwide. The present study attempted to evaluate the suitable conditions for the synthesis of PMD from two sources of materials that are pure (±)-citronellal (∼ 96%) and lemon eucalyptus (Eucalyptus citriodora) essential oil (∼ 60% citronellal) by treatment of sulfuric acid in a biphasic medium (H2O/essential oil). The one-factor-at-a-time method was used to determine the optimal conditions for the synthesis of PMD from pure (±)-citronellal. The effect of various factors such as oil-to-water ratio (citronellal to sulfuric acid aqueous solution), acid concentration (sulfuric acid), reaction temperature, and reaction time on the PMD yield and conversion of citronellal was investigated. The highest PMD yield (95.6%) with excellent conversion of citronellal (98.5%) was obtained at optimal conditions such as, oil to water ratio of 1:2, acid concentration of 0.75% (w/w), reaction temperature of 60°C, and reaction time of 6 h. These optimal conditions were applied to synthesize PMD from Eucalyptus citriodora essential oil. From 200 grams of essential oil and applied optimal conditions, PMD was obtained with a yield of 91.5%.

One-Pot Transformation of Citronellal to Menthol Over H-Beta Zeolite Supported Ni Catalyst: Effect of Catalyst Support Acidity and Ni Loading

Citronellal was converted to menthol in a one-pot approach using H-Beta zeolite-based Ni catalyst in a batch reactor at 80 °C, under 20 bar of total pressure. The effects of H-Beta acidity (H-Beta-25 with the molar ratio SiO2/Al2O3 = 25 and H-Beta-300 with SiO2/Al2O3 = 300) and Ni loading (5, 10 and 15 wt %) on the catalytic performance were investigated. Ni was impregnated on H-Beta support using the evaporation-impregnation method. The physico-chemical properties of the catalysts were characterized by XRD, SEM, TEM, ICP-OES, N2 physisorption, TPR, and pyridine adsorption–desorption FTIR techniques. Activity and selectivity of catalysts were strongly affected by the Brønsted and Lewis acid sites concentration and strength, Ni loading, its particle size and dispersion. A synergetic effect of appropriate acidity and suitable Ni loading in 15 wt.% Ni/H-Beta-25 catalyst led to the best performance giving 36% yield of menthols and 77% stereoselectivity to ( ±)-menthol isomer at 93% citronellal conversion. Moreover, the catalyst was successfully regenerated and reused giving similar activity, selectivity and stereoselectivity to the desired ( ±)-menthol isomer as the fresh one.Graphical

Heterogeneous Catalytic Conversion of Citronellal into Isopulegol and Menthol: Literature Review

The conversion of citronellal into isopulegol is a key route in the production of a number of important chemicals. In the perspective of green conversion, the use of a heterogeneous catalyst is superior due to its ease in separation and reusability, so it facilitates a highly economical conversion. In this review, we examine the use of some transition metals in cyclization reactions, which are suitable for citronellal conversion into isopulegol, and consider the potential progress in clay-based catalysts. The structure of clay which potentially provides the porosity by modification and supporting active metal is proposed to be the low-cost catalyst for the conversion. As other mechanism by porous materials-supported metal, the porosity of clay support contributes to conduct thesurface adsorption mechanism and the Broensted acid supply, meanwhile the metal acts as active site for cyclization, and in the one-pot conversion into menthol, as both cyclization and hydrogenation.

Fe-Modified Zeolite BETA as an Active Catalyst for Intramolecular Prins Cyclization of Citronellal

Prins intramolecular cyclization of citronellal giving desired product isopulegol was performed using different modified zeolites BETA (Si/Al ratio 25, 38 and 75 modified with iron or zinc of 1, 5 or 10 wt.% by wet impregnation method). In case of materials BETA Si/Al 38 and 75 led material impregnation with metal to increase of material catalytic activity (accompanied with increase of amount of weak acid sites detected using temperature programmed desorption). Material BETA 38 with loading 1 wt.% of Fe provided 97% citronellal conversion and 94% selectivity of isopulegol formation (90 °C, toluene, 24 h).

Microwave-assisted synthesized porous clay heterostructure-Zn/Si from montmorillonite for citronellal conversion into isopulegol

Microwave-assisted synthesis method was applied for producing porous clay heterostructure-Zn/Si heterostructure from Indonesian natural montmorillonite. The porous montmorillonite heterostructure was prepared by previously intercalating cetyl trimethyl ammonium as templating agent and surfactant, and trimethyl ammonium hydroxide as co-surfactant, followed by the introducing Zn–Si precursor solution for the sol-gel reaction of porous formation. The comparison of the use of microwave-assisted synthesis and hydrothermal method for the porous formation was studied. Physicochemical characterization by using XRD, SEM-EDX, TEM, gas sorption analysis, and FTIR method. Effect of the evolution of the surface characters on its catalytic activity in citronellal conversion into isopulegol was studied. The characterization by XRD informed the increasing basal spacing d001 from 1.57 nm into 3.71 nm by the microwave-assisted method, meanwhile the hydrothermal method produced 3.56 nm spacing. The increasing specific surface area from 98.82 m2 g−1 into 752.95 m2 g−1 and 409.95 m2 g−1 for microwave-assisted synthesized and hydrothermal synthesized composites, were obtained. These profiles are attributed to the increasing surface acidity determined by pyridine-adsorption method and n-butylamine titration method, and contributed to the significant increasing catalytic activity. The time-efficient synthesis method obtained by the microwave-assisted method is good alternative for the preparation of highly active montmorillonite heterostructure composite for acid-catalyzed organic reaction.

Tungsten oxide-based materials as effective catalysts in isopulegol formation by intramolecular Prins reaction of citronellal

Several types of mixed WO3/SiO2/Al2O3 materials were prepared using sol–gel and wet impregnation methods. Four different loadings of WO3 (1, 10, 25 and 40 wt%) were prepared. Materials were characterized using X-ray diffraction, X-ray fluorescence spectroscopy, and their acidity was measured by temperature programmed desorption of pyridine. Catalytic activity of these materials was tested in Prins reaction—intramolecular cyclization of citronellal. Influence of reaction conditions (temperature 70–90 °C, catalyst amount 1–10 wt%, catalyst type) on citronellal conversion and selectivity of isopulegol formation was monitored. The best result (90% of isopulegol, 97% selectivity of isopulegol formation, 24 h) was obtained using W25 IMP catalyst (10 wt%, 50 °C). Possibility of catalyst reuse was confirmed.

ZnO-Porous Clay Heterostructure from Saponite as Green Catalyst for Citronellal Cyclization

Green conversion in organic synthesis is one of the interesting and important topics in green chemistry. The use of heterogeneous catalysis instead of homogeneous catalysis offers some advantages, such as easy separation and reusability. In this research, a heterogeneous acid catalyst was prepared from saponite by immobilizing ZnO in the form of a pillared clay (Zn/PILS) and Zn supported on porous clay heterostructure (Zn/PCH). Physicochemical studies involving X-ray diffraction measurement, surface analysis using a gas sorption analyzer, and surface acidity measurement were performed. Results indicated that the increasing surface acidity and the high specific surface area of the material were the relevant physicochemical properties that facilitate environment-friendly citronellal cyclization. The higher values for both parameters in Zn/PCH than in Zn/PILS linearly affected citronellal conversion and the selectivity for isopulegol production. Zn/PCH demonstrated a conversion rate of 98.9% for a 3-hour reaction and a selectivity of 100% for isopulegol production, and it exhibited reusability properties. Copyright © 2020 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Catalytic conversion of citronellal to citronellol over skeletal Ni catalyst

Catalytic conversion of citronellal to citronellol was performed via hydrogenation over skeletal Ni catalyst. The reaction parameters applied include variation of reactant-catalyst ratio, reaction temperature, pressure, and time. Citronellal 78 % obtained from the fractionation of citronella oil was used as the reactant. The reaction was carried out using reactant-catalyst ratio of 1:5 % and 1:10 % at temperatures of 100 °C, 150 °C and 200 °C and pressure of 10 bar, 15 bar and 20 bar for 1 and 3 hours. Results show that the optimum reaction condition was at 100 °C with reactant-catalyst ratio of 1:10 % under pressure of 20 bar for 1 hour giving 100 % conversion of citronellal, 51.78 % yield of citronellol and 40.39 % selectivity.

Nickel Supported Natural Zeolite as a Bifunctional Catalysts for Conversion of Citronella Oil Crude to Menthols

Characterization and catalytic activity of modified natural zeolite for the conversion of citronella oil to menthol was investigated. In this research, natural zeolite was prepared by acid activation with HCl and impregnated with Ni metal. The addition of Ni metal of around 12.5 nm in diameter provided a bifunctional catalyst for two steps of citronella oil conversion i.e. cyclization and hydrogenation. The process was performed in a one-pot reaction system by stirring at 200oC with pressure of 20 bar H2 for 3h. The reaction products changed slightly with varieties of reaction temperature and amount of catalysts employed. Results showed that Ni/NZB-HT catalyst was the best catalyst which was able to convert citronella oil to menthol with a selectivity of 50% menthol and 100% conversion of citronellal.

Novel sulphated zirconia pillared clay nanoparticles as catalyst in microwave assisted conversion of citronellal

Preparation of novel sulphated zirconia pillared montmorillonite and saponite clays nanoparticles (SZ/MMT and SZ/SAP) were studied to find a highly active, economist and environment friendly catalysts in the conversion of citronellal into menthol. Sulphated zirconia pillared MMT was prepared by direct sulphation into zirconia pillared MMT, which is a new and fast technique. Comparative study also conducted by evaluating the activity of SZ/MMT with sulphated zirconia nanoparticle (SZ). Material characterisation was performed by X-ray diffraction, Brunauer–Emmett–Teller surface area analysis, scanning electron microscope and also surface acidity by mean pyridine adsorption Fourier transform infrared analysis and total acidity by butylammine titration. Catalytic activity of both SZ/MMT and SZ/SAP was observed in a reaction of citronellal conversion. The operation parameters consist of technique of reaction; tandem cyclisation–hydrogenation and catalytic hydrogen transfer mechanism were investigated. The results show that the pore size of catalyst and the presence of surface acidity affect significantly to increase the isomerisation as well as hydrogenation mechanism. The catalytic hydrogen transfer over microwave irradiation was observed as the more efficient process compared to the tandem cyclisation–hydrogenation from the selectivity of the product and also the other factor influencing the surface mechanism. In another aspect, the results clearly indicated the reusable properties of the sulphated zirconia pillared clay catalysts under varied conditions. Correlation between physicochemical characters and the reaction mechanism is discussed in this study.

Ni Dispersed on Sulfated Zirconia Pillared Montmorillonite as Bifunctional Catalyst in Eco-Friendly Citronellal Conversion

Nickel dispersed on sulfated zirconia pillared montmorillonite was prepared by three main steps; zirconia pillarization, sulfation and nickel dispersion. The synthesized material was characterized with FTIR spectroscopy, elemental analysis, x-ray diffraction and gas sorption analyzer before was tested for microwave assisted citronellal conversion via catalytic hydrogen transfer mechanism. The results showed that the obtained material gave high total conversion and demonstrated cyclization, isomerization and hydrogenation mechanism in one pot reaction. The presence of sulfate and nickel in the catalyst play important role within the mechanism.

Preparation, Characterization and Catalytic Activity of Sulfated Zirconia by Varied Sol-Gel Method

The sulfated zirconia catalysts were was prepared by sol–gel processes consist of varied templating method. Both preparations consist of sol-gel synthesis of zirconium dioxide followed by sulfatation process by using NH4SO4 solid reaction method. Two different templating agent; urea and cetyltrimetyl ammonium bromide was used in sol-gel processes. The prepared material was characterized using scanning electron microscope (SEM), x-ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) measurements. From the XRD measurement it can be concluded that both materials consist of ZrO2 in combined phases while from BET surface area analysis it can be noted that material prepared by urea template has higher specific surface area compared to that use CTAB template. Both materials exhibit the activity as acid catalyst in microwave assisted conversion of citronellal. It is also confirmed that the higher the surface area the higher total conversion of citronellal obtained. Study on the correlation between physicochemical properties of materials with the catalytic activity was discussed in this paper.

Effect of Sulfation on Zirconia-Pillared Montmorillonite to the Catalytic Activity in Microwave-Assisted Citronellal Conversion

Preparation of sulfated zirconia-pillared montmorillonite was carried out in two steps; zirconia pillarization and sulfation to zirconia-pillared montmorillonite. The prepared materials were characterized by using X-ray diffraction (XRD), measurement of the specific surface area, total pore volume and pore size distribution by the N2adsorption method, scanning electron microscopy-energy dispersive X-ray (SEM-EDX), and surface acidity determination by using pyridine adsorption-FTIR analysis. The activity of the materials as catalysts was evaluated for a microwave-assisted conversion of citronellal. The results showed that the prepared materials had a physicochemical character that promoted high catalytic activity to convert citronellal. From varied Zr content and study of the effect of sulfation on the activity, it was found that Zr content and sulfation increase the surface acidity of the material as shown by the higher total conversion and tendency to produce menthol as a product of the tandem cyclization-hydrogenation mechanism.

Substrate specificity of a novel squalene-hopene cyclase from Zymomonas mobilis

Abstract Squalene-hopene cyclases (SHC; EC 5.4.99.17) catalyze the cyclization of triterpenoids via cationic intermediates in one of the most complex reactions known in biochemistry. In this study, we report the functional expression of a novel SHC from the ethanol producing bacterium Zymomonas mobilis (ZmoSHC1; YP_163283.1). Biochemical characterization of ZmoSHC1 uncovered unique substrate activity patterns compared to the previously reported AacSHC from Alicyclobacillus acidocaldarius and ZmoSHC2, the second squalene-hopene cyclase from Z. mobilis. ZmoSHC1 showed cyclization of the non-natural substrates homofarnesol (C16) and citronellal (C10) in addition to hopene formation from squalene (C30). Moreover, ZmoSHC1 turned out to reveal high biocatalytic stability during long-term incubations. Remarkably, ZmoSHC1 exhibited a shift of activity towards substrates of shorter chain lengths, displaying over 50-fold higher conversion of homofarnesol and more than 2-fold higher conversion of citronellal in comparison to squalene conversion.

MOFs as multifunctional catalysts: One-pot synthesis of menthol from citronellal over a bifunctional MIL-101 catalyst

A bifunctional MOF catalyst containing coordinatively unsaturated Cr(3+) sites and palladium nanoparticles (Pd@MIL-101) has been used for the cyclization of citronellal to isopulegol and for the one-pot tandem isomerization/hydrogenation of citronellal to menthol. The MOF was found to be stable under the reaction conditions used, and the results obtained indicate that the performance of this bifunctional solid catalyst is comparable with other state-of-the-art materials for the tandem reaction: Full citronellal conversion was attained over Pd@MIL-101 in 18 h, with 86% selectivity to menthols and a diastereoselectivity of 81% to the desired (-)-menthol, while up to 30 h were necessary for attaining similar values over Ir/H-beta under analogous reaction conditions.

Oxidation of Citronellal to Citronellic Acid by Molecular Oxygen Using Supported Gold Catalysts

The oxidation of citronellal to citronellic acid was studied using molecular oxygen as oxidant and gold-containing supported catalysts under aqueous conditions. The reactions were carried out at 60-90 degrees C, with 200 Nml min(-1) O2 and at pH values from 9 to 12. The alumina- or titania-supported catalysts were synthesized according to the deposition-precipitation procedure using urea or NaOH. Mechanistic studies have revealed that radical-initiated reactions lead to undesired by-products especially at pH <9, that is, the C=C bond is attacked and a diol is primarily formed probably via an epoxide intermediate. This side reaction can be suppressed to a large extent by increasing the pH to 12 and by raising the catalyst/oxygen ratio. Furthermore, detailed studies on the influence of reaction time, pH value, reactant concentration and amount of catalyst show that citronellic acid can be obtained in over 90% yield with total conversion of citronellal at pH 12 and a temperature of 80 degrees C.

Pd–heteropoly acid as a bifunctional heterogeneous catalyst for one-pot conversion of citronellal to menthol

Pd–H3PW12O40/SiO2 catalyzes the one-pot transformation of (+)-citronellal to menthol via acid-catalyzed cyclization followed by Pd-catalyzed hydrogenation, with 92% yield of menthol at 100% citronellal conversion and 85% stereoselectivity for the desired (−)-menthol.

Cyclization of citronellal over zeolites and mesoporous materials for production of isopulegol

Cyclization of (+)-citronellal was investigated over zeolites and mesoporous materials as well as on silica under a nitrogen atmosphere in cyclohexane as a solvent. The highest cyclization rates were observed over mesoporous materials and 12-membered ring zeolites with high Brønsted acid concentration, while very low cyclization rates were achieved over silica with low or no Brønsted acidity, respectively. At the same a time low cyclization rate was observed over 10-membered ring pore H-ZSM-5 with a high Brønsted acid site concentration, which is due to diffusional limitation of the product in the narrow pores. The selectivity to cyclization products was very high over all the catalysts, being independent of the conversion of citronellal. Neither concentration of the Brønsted nor Lewis acid sites influenced the stereoselectivity to isopulegol. The support structure had only a minor effect on the stereoselectivity. Quantum mechanical calculations were carried out to explain the experimental results. The calculated stabilities of the carbocationic reaction intermediates correlated well with the observed stereoselectivity. The stereoselectivities were analogous when starting from racemic citronellal mixture or enantiopure (+)-citronellal; the former one gave 8 different pulegols, whereas only 4 pulegols were formed from (+)-citronellal.